1. Field of the Invention
The invention relates in general to a method and a structure for changing a scanning resolution. The method and the structure can be adapted for an optical scanner. Using the method and the structure, excepting a normal scanning mode, the other scanning mode of a high resolution can be chosen to operate the optical scanner.
2. Description of Related Art
With improvement of computer performance and high development of multimedia technology, analog-based images of words or patterns can be captured using an optical scanner, then transformed into digital signals. As a result, after the process of transforming the analog-based images into the digital signals, an image file can be showed, identified, edited, saved or output by a computer or other instruments.
According to the ways to input document image, an optical scanner can be categorized into a packet scanner, a sheet-feed scanner, a drum scanner, a flatbed scanner and so on. The flatbed scanner is most popular among them because it can provide a scanning image with a stable quality, it can provide a function of scanning a reflection document or a transparent document, and, further, it is provided with an automatic document feeder (ADF) to scan a stack of documents with a same size.
In general, the flatbed scanner is provided with a piece of transparent glass on which a to-be scanned document, such as a negative plate, a projection document a reflection document, is placed. A scanning chassis positioned in the flatbed scanner is linearly driven using a chassis-positioned mechanism and a chassis-driven mechanism. Analog-based image signals on a surface of a document can be scanned step by step using the scanning chassis. Finally, digital image signals can be transfonned from the analog-based image signals and output.
Referring to FIG. 1A, FIG. 1A is a schematic view showing a motion of a conventional scanning chassis. A scanning chassis 10 scanning based on a scanning line 12 can move in a scanning direction 14 and can scan a document on the scanning chassis 110 step by step. The scan line 12 is perpendicular to the scanning direction 14.
Referring to both FIG. 1A and FIG. 1B, FIG. 1B is a schematic view showing an area scanned by a scanning chassis scanning based on a scan line, the width of which is “A”, with a scanning chassis moving a distance “B” in a scanning direction according to a motion of a conventional scanning chassis shown in FIG. 1A. The number (PN1) of total pixels in the scanning area divided by the total scanning area (AD1) equals the number (PUN1) of pixels in a unit scanning area, i.e. PN1/AD1 =PUN1, where AD1=A*B. In the prior art, the scanning chassis 10 scans in a normal mode where a right angle exists between the scan line 12 and the scanning direction 14. In the above-mentioned normal mode, in order to enhance the resolution that the scanning chassis 10 scans a document, the number (PUN1) of pixels in a unit scanning area should be increased. For example, to achieve the objective, an image sensor with a high resolution can be used. However, the cost of the image sensor with a high resolution is high.